Hearing loss is common in newborns, affecting 1 to 3 out of every 1,000 normal births. It is the most common birth defect and significantly impacts development. Early identification is crucial because hearing plays a foundational role in speech, language, and learning. Addressing hearing loss promptly can mitigate long-term effects on communication and cognitive growth.
Genetic Predisposition
Up to 80% of newborn hearing loss has a genetic origin, inherited through autosomal recessive, autosomal dominant, and X-linked patterns. Autosomal recessive inheritance accounts for 75-80% of non-syndromic genetic hearing loss, requiring both parents to carry a mutated gene.
Autosomal dominant inheritance, needing one mutated gene copy, accounts for 19% of non-syndromic cases. X-linked patterns are less common, making up less than 1%. Mutations in the GJB2 gene, important for inner ear function, are a frequent cause of severe non-syndromic hearing loss. A family history of hearing loss can indicate a genetic predisposition.
Some genetic syndromes include hearing loss. Usher syndrome, an autosomal recessive condition, combines hearing loss with progressive vision impairment. Waardenburg syndrome, often autosomal dominant, can present with varying degrees of hearing loss and changes in skin, hair, and eye pigmentation. Pendred syndrome is another autosomal recessive disorder linked to hearing loss and thyroid abnormalities.
Influences During Pregnancy and Birth
Factors during pregnancy and birth influence newborn hearing. Prenatal infections, grouped as TORCH (Toxoplasmosis, Syphilis, Rubella, Cytomegalovirus, Herpes simplex virus), cause congenital hearing loss. Cytomegalovirus (CMV) is the most common non-hereditary cause of sensorineural hearing loss, accounting for up to 10% of cases. Many CMV-infected newborns are asymptomatic at birth but may develop hearing loss later or experience progressive impairment.
Maternal health conditions during pregnancy contribute. Uncontrolled gestational diabetes mellitus (GDM) is associated with higher hearing screening referrals and an increased risk of bilateral sensorineural hearing loss. Preeclampsia, characterized by high blood pressure and organ damage, is associated with transient hearing loss at lower and mid-frequencies.
Maternal exposure to ototoxic medications during pregnancy affects fetal hearing. Certain antibiotics, such as aminoglycosides, can cause irreversible bilateral congenital deafness. Valproic acid and low-dose acetylsalicylic acid have also been linked to hearing impairment.
Prematurity and low birth weight are factors. Premature infants, especially those under 1500 grams, have an increased risk due to immature organ development and susceptibility to complications like hypoxia and jaundice. Severe jaundice poses a risk as high levels of unconjugated bilirubin can be toxic to the auditory pathway, affecting the brainstem and auditory nerve. Birth complications like lack of oxygen (asphyxia) or severe head trauma can also lead to sensorineural hearing loss due to inner ear or auditory pathway damage.
Factors Developing After Birth
Postnatal infections, particularly bacterial meningitis, are a concern. Meningitis, an inflammation of the membranes surrounding the brain and spinal cord, can lead to sensorineural hearing loss by affecting the cochlea or auditory nerve. This complication can profoundly impact communication skills, especially if it occurs before language development.
Certain medications administered to newborns after birth are ototoxic, as they damage the auditory system. Aminoglycoside antibiotics, such as gentamicin, amikacin, and kanamycin, are frequently used to treat serious bacterial infections, particularly in neonatal intensive care units (NICUs). These drugs can cause irreversible hearing loss by damaging inner ear hair cells, initially affecting high-frequency hearing.
Loop diuretics, another medication class, are prescribed for critically ill neonates and can contribute to hearing loss. While they may cause reversible hearing loss by blocking ion transport in the cochlea, they can increase the risk and severity of aminoglycoside-induced permanent hearing loss when administered concurrently. Head trauma in infancy can lead to hearing impairment. Prolonged exposure to excessive noise, such as in a NICU, is a theoretical risk factor, though measures are typically in place to mitigate this.
Newborn Hearing Screening
Universal newborn hearing screening is typically performed before a baby leaves the hospital, ideally within the first month of life. Its purpose is to enable early detection and intervention, crucial for a child’s speech, language, and cognitive development.
Newborn hearing screening uses two primary methods: Otoacoustic Emissions (OAEs) and Automated Auditory Brainstem Response (AABR) tests. OAEs measure echoes produced by outer hair cells in the inner ear (cochlea) in response to sounds. If hearing is normal, an echo is reflected back and measured. AABR testing measures responses from the inner ear and auditory brainstem as sound travels to the brain, using electrodes and earphones. A “pass” result indicates normal hearing, while a “refer” or “fail” suggests further testing is needed.
If a newborn does not pass the initial screening, a rescreening is performed, followed by a comprehensive diagnostic evaluation by an audiologist if needed. Early identification of hearing loss, ideally before six months of age, allows for timely intervention, such as hearing aids, cochlear implants, and speech-language therapy. This prompt action significantly improves language outcomes and overall development.